Ultra high frequency oscillator device



DLHHDH KUUM y 1 A. M. GUREWITSCH 2,476,725

ULTRA HIGH FREQUENCY OSCILLATOR DEVICE Filed Aug. 28, 1944 Inventor:Anatole MGurew'ltsch W im/ His Attorney.

Fatented July 19, 1949 UNITED DEHKUH KUUNE STATES PATENT OFFICE VICEAnatole M. Gurewitsch, Schenectady, N. Y., assignor to General ElectricCompany, a corporation of New York Application August 28, 1944, SerialNo. 551,467

8 Claims. (01. 315-39) The present invention relates to high frequencyapparatus and is primarily concerned with the provision of an improvedoscillator of the type which employs a discharge device or tube, such asa vacuum triode, as an exciting element.

In my copending application, Serial No. 471,973, filed January 11, 1943,now U. S. Patent No. 2,443,- 907, granted June 22, 1948, and assigned tothe assignee of the present application, there is disclosed anoscillator in which a vacuum triode arranged within a cavity-formingstructure has connected with the grid of the triode a conductive memberwhich is adapted to form a continuous wave-guiding path between thegrid-anode gap of the triode and its grid-cathode gap. When this path isgiven appropriate length and proportions, the feedback effectsattributable to it are readily fixed at the proper phase and amplitudeto assure the efficient generation of selfsustained oscillations. It isan object of the present invention to provide a new and improvedoscillator of the above type for producing longer wave lengths whileretaining a small size of the oscillator structure.

It is another object of the present invention to provide a new andimproved ultra high frequency oscillator operable at a plurality ofdiscrete frequencies.

It is a still further object of the present invention to provide a newand improved feedback circuit for a re-entrant ultra high frequencyoscillator.

Briefly, the invention makes use of a multiply folded coaxialtransmission line arrangement providing a plurality of concentrictransmission line sections connected in series between the anode-gripgap and the grid-cathode gap of a triode used in a. re-entrant typeoscillator. In order to obtain oscillations at predeterminedfrequencies, the lengths of the sections of the coaxial transmissionline are properly adjusted to act either as a single resonatorcorresponding to the length of the sections in series or as a resonatorcorresponding to the length of any one or more of the sections.

The features of the invention desired to be protected herein are pointedout in the appended claims. The invention itself, together with itsfurther objects and advantages, may best be understood by reference tothe following description taken in connection with the accompanyingdrawing in which the single figure is a 1ongitudinal sectional view of ahigh frequency oscillator embodying the invention.

Referring to the drawing, there is shown an ultra high frequencyoscillator having a threeelectrode discharge device I as its centralelement. This tube comprises a cylindrical anode 2, a grid 3 and acylindrical cathode 4 having its emissive part in the form of a flatdisk surface 5 which faces the grid 3. The envelope within which theseelectrodes are enclosed comprises a series of three circular metal parts6, l, 8 which are supported in mutually spaced relation by glasscylinders 9, I0 sealed between them. The part I provides a terminal forthe grid 3. A terminal for the anode is provided by a cylindricalenlargement II which is welded or soldered against the upper surface ofthe disk 6. The cathode 4 is provided at its lower extremity with aflange I2 which parallels the under surface of the part 8, but which isseparated from that part by an insulating spacer I3 which may be, forexample, a mica washer. With this arrangement, the part 8 has a highfrequency connection with the cathode through the capacity existingbetween this part and the flange I2, but is effectively insulated fromthe cathode so far as direct current is concerned. Separate directcurrent connections are made to the cathode by means of lead-in wiresI4, secured to the under surface of the part I2 and terminally connectedto prongs I5 which depend from the base of the discharge tube.Additional prongs l6 and lead-in wires H are provided for the purpose ofsupplying heating current to the coiled filament I8 arranged within thecathode cylinder 4 so that the emissive part of the filament can bemaintained at an elevated temperature by this means.

The oscillating system in which the tube I is incorporated comprises acavity-forming structure having, as a principal component, an elongatedconductive (e. g. copper or brass) preferably silVer-plated cylinder I9.This surrounds the tube I and is symmetrical with respect to the axis ofalignment of the electrodes of the tube. A conductive wall part 20extends across one end of the cylinder I9 and provides a mount for thebase of the cylinder 2. In addition, the wall part 20 bears upon theexposed surface of the lower portion of the part 8 and is thuseffectively connected with the cathode 4 so far as high frequencycurrents are concerned by capacity coupling through the insulatingspacer I3. A corresponding connection to the anode is made by a solidlongitudinal cylindrical conductor 2| which is supported within thecylinder I9 by means of a transverse wall part 22 and which is providedat its inner extremity with contact 3 fingers 23 and 24 arranged toengage the anode end of the tube I both at the terminal tap II and atthe periphery of the disk 6.

The grid terminal 1 is peripherally connected to a tubular conductor 25which extends longitudinally of and concentric with the cylinder I9.Mounted concentric with the tubular conductor 25 is a conductivecylinder 26 having a transverse end wall 21 connected to the outersurface of the conductor 25 for supporting the cylinder 26 in concentricalignment with the conductor 25. A terminal wire 28, which extendsthrough an insulating washer 29 provided in a wall of the cylinder I9,is connected to the outer surface of the conductor 26 to provide anexternal connection with the grid terminal 'I for supplying controlpotentials thereto. Mounted concentrically between the parallel tubularconductors 25, 26 is a tubular conductor 30 which is supported from thecylindrical conductor 2| by means of a transverse wall portion 3|.

The connections for unidirectional potential for the triode I may bemade in various ways. In the arrangement illustrated, the anode isassumed to be at ground potential (i. e., at the potential of theconductive structure as a whole), while the cathode is insulated (in aD. C. sense) from the main conductive structure by the spacer l3 and ismade negative with respect to the anode by an appropriate connection tothe contact prongs I5. The grid connection is made through the conductor28 and, if a cathode bias arrangement is to be employed, the connectionshould be made to the terminal 32 and resistor 33 adjusted to give thebias which is required for mosteffective operation.

Like any confined space bounded by a conductive medium, the chamberenclosed by the cylinder l9 provides a system which may be made toresonate electrically at a particular frequency determined by thedimensions and configuration of the chamber and of the elements enclosedby it. This means that, under appropriate conditions, electro-magneticwaves may be caused to exist within the chamber in a space distributionfixed by the nature and location of the exciting source and by theboundary conditions set by the form of the conductive structure.

The effective electrical impedance and inductance loss ratio of aspace-resonant structure of the type under consideration are high enoughso that a structure of this kind can be made to serve as a tank circuitof an oscillator having an intended operating frequency which is thesame as, or is harmonically related to, the resonant frequency of thespace enclosed by the structure. Since resonant frequency is a directfunction of the resonators in question, it may be varied withinreasonable limits by appropriate adjustment of these dimensions. Topermit such adjustment in connection with the structure illustrated inthe drawing, there is provided a plunger 34 having two sets of contactfingers 35, 36 which, respectively, bear upon the opposed surfaces ofthe parts 9 and 2|. This plunger may be moved back and forth by anyexternally accessible actuating rods 31 and, by this means, the size ofthe cavity resonator may be adjusted as desired.

In the oscillator illustrated, the triode comprises a means for excitingthe resonant system provided by the cylinder l9. If voltage variationscan be caused to occur between the grid and anode of the tube at theresonant frequency of cylindrical structure H! (as modified by thepresence of the tubular conductors 25, 26, 30, the solid cylinder 2|,and the tube itself), electromagnetic waves of the frequency in questionwill be established in a cavity-forming space. Such waves may beconsidered as being initiated in the vicinity of the grid-anode gap andas being propagated from this point throughout the remainder of thecavity. Their path of propagation is governed in the first instance bythe presence of the conductive tubes 25, 26, 30 and transverse Walls,3|, 2'! which necessarily tend to confine or guide the waves along themultiply folded path between the cylindrical conductors. At theextremity of the tube 26, however, the waves are free to pass throughthe gap indicated at 38. Viewing the mechanism of wave propagation asbeing a condition of energy flow, it is seen that wave energy issuingfrom the gap 38 can flow in the reverse direction along the outside ofthe conductor 26 toward the vicinity of the cathode to grid gap of thetriode At this point, a variable electric field can be established inaccordance with the properties of waves of the type under consideration.

The feedback path between the anode-grid gap and the cathode-grid gap ofthe device I, as previously stated, consists of three sections ofconcentric transmission line connected in series and formed,respectively, between tubular conductor 25 and the cylindrical conductor2|, the outer surface of the conductor 25 and the inner surface oftubular conductor 30, and finally the outer surface of conductor 2| andthe inner surface of the conductor 26. If all three sections areproperly adjusted in length, they will act as a single resonatorcorresponding in length to the three sections in series. This singleresonator functions as an anode tank circuit for the device I and thecavity resonator constituted by the member 9 may be tuned by adjustmentof plunger 34 to the frequency of this tank circuit.

The gap 38, as well as the transverse walls 21, 3| in the feedback pathbetween the grid-anode gap and cathode-grid gap, representdiscontinuities in the path of propagation of Waves originating at theformer gap. In accordance with principles well understood in theelectronics are, some reflection of the wave energy will occur at eachof these discontinuities. Depending upon matching conditions ofimpedances of the discontinuities, a single section of the foldedfeedback path, for instance the section comprising the inner surface ofthe tubular conductor 25 and the outer surface of the cylindricalconductor 2|, may be made to act as the anode tank circuit of the tubeLikewise, this particular concentric line section, in series with theconcentric line section constituted by the tubular conductors 25, 3|],may be used as theanode tank circuit of the tube I. It is apparent,therefore, that the multiply folded concentric transmission linesections may be used as tank circuits for at least three differentfrequencies. At each particular frequency, exact tuning of the cavityresonator constituted by the member I9 is obtained by adjustment of theplunger 34.

In order that high frequency energy may be taken from the oscillator forutilization in an external circuit, there is provided a coupling loop 39which extends into the cavity and which is supported from a hollowtubular conductor 40 extending outwardly through the plunger 34 and theend wall 22. A conductor 4|, which connects with one extremity of thecoupling loop 39, is arranged within the tubular conductor 40 and formswith it a coaxial transmission line.

An important advantage of the oscillator structure described lies in thefact that the multiply folded resonator permits the construction of anoscillator operable over a plurality of different wave lengths, thelongest wave length being several times the length of the shortest wave,but which still retains the small over-all dimensions of a re-entranttype oscillator. By proper matching of impedances throughout the lengthof the folded transmission line sections, it has been found that anoscillator of this type may be operated at frequencies having wavelengths of centimeters, centimeters, and 30 centimeters. At each ofthese frequencies, satisfactory tuning of the cavity resonator structureis obtained by a small adjustment of the position of the plunger 34.

While the invention has been described by reference to a particularembodiment thereof, it will be understood that numerous modificationsmay be made by those skilled in the art without departing from theinvention. For example, more than three sections of folded transmissionline may be employed to provide a greater number of predeterminedfrequencies of oscillation. I, therefore, aim in the appended claims tocover all such equivalent variations as come within the true spirit andscope of the foregoing disclosure.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A high frequency oscillator comprising a cavity resonator defined bya hollow conductive structure, an electric discharge device within saidresonator comprising a plurality of electrodes including a cathode, ananode and a grid defining anode-grid and grid-cathode gaps, couplingmeans between said anode-grid and grid-cathode gaps of said dischargedevice comprising a plurality of sections of concentric transmissionline concentrically arranged and connected in series, said line beingcoupled at one end to the anodegrid gap of said device and at its otherend to said resonator, said conductive structure comprising anadjustable end wall for controlling the resonant frequency of saidresonator.

2. An ultra high frequency oscillator for operation at a plurality ofpredetermined frequencies comprising a cavity resonator defined by aconductive cylinder, an electric discharge device in said cylindercomprising a plurality of electrodes including an anode, a cathode and agrid defining anode-grid and grid-cathode gaps, means connecting saidcathode and said anode to spaced points on said resonator, and couplingmeans defining a waveguiding path between the anodegrid gap andgrid-cathode gap of said discharge device comprising a plurality ofsuccessively telescoped coaxial conductors connected to provide aplurality of concentrically arranged concentric transmission linesections connected in series, said resonator including an adjustable endwall for controlling the resonant frequency thereof.

3. An ultra high frequency oscillator comprising a cavity resonatordefined by av conductive cylinder, an electric discharge device withinsaid resonator including a plurality of electrodes comprising a anode, acathode and a grid defining anode-grid and grid-cathode gaps, meansconnecting said cathode to said cylinder, a longitudinal cylindricalconductor connected to said anode and coupling means defining awaveguiding path between the anode-grid and grid-cathode gaps of saiddischarge device comprising a pair of concentrical cylindrical membersof different diameters connected to said grid, the inner of saidcylinders eiitending an appreciable distance along said longitudinalconductor but spaced therefrom and the outer of said cylinders beingsupported from said inner cylinder by a transverse metallic wall, and aconductive cylinder concentric to said longitudinal conductor andsupported therefrom extending an appreciable distance between said pairof concentric cylindrical members to define therewith a plurality ofconcentrically arranged concentric transmission line sections connectedin series.

4. An ultra high frequency oscillator comprising a conductive memberdefining a cavity res0nator,an electronic tube within said resonatorincluding an anode, a cathode and a grid defining anode-grid andgrid-cathode gaps, a cylindrical conductor connected to said anode,coupling means providing a Waveguiding path between the anode-grid andgrid-cathode gaps of said tube comprising a pair of longitudinalcylinders connected to said grid and an intermediate longitudinalcylinder connected to said conductor, said cylinders defining aplurality of concentrically arranged concentric transmission linesections connected in series.

5. A high frequency oscillator comprising, a conductive structuredefining a resonator, an electric discharge device including an anode, acathode and a grid supported in mutually spaced and insulated relationwithin said structure and defining a grid-anode gap and a grid-cathodegap, said anode and cathode having respectively high frequencyelectrical connections with spaced points of said structure, a pluralityof concentric cylinders of progressively increasing diameters, alternateones of said cylinders being connected with said grid and said anode andwith the free ends thereof extending in oppositely directed andoverlapping relation to provide a plurality of concentrically arrangedtransmission line sections defining a waveguiding path from thegridanode gap of said device to the grid-cathode gap of said device,which is folded back on itself.

6. A high frequency oscillator comprising, a cavity resonator defined bya conductive cylinder, an electric discharge device within saidresonator including an anode, a cathode and a grid supported in mutuallyspaced and insulated relation to define grid-anode and grid-cathodegaps, a cylindrical conductor connected with said anode and to saidconductive cylinder, means connecting said cathode with said conductivecylinder, a plurality of concentric cylinders of progressivelyincreasing diameters, alternate ones of said concentric cylinders beingconnected respectively with said grid and said cylindrical conductor todefine therebetween a waveguiding path which is folded back on itselffor guiding electromagnetic waves from the grid-anode gap to thegrid-cathode gap of said device and thereby sustain regenerativeoscillations.

7. High frequency apparatus comprising a cavity resonator, an electricdischarge device within said resonator having a plurality of electrodesincluding a cathode, a grid, and an anode defining cathode-grid andanode-grid gaps, a structure comprising at least two concentriccylinders having a common closed end at one end thereof and at least onecylinder having a closed end and concentrically intermeshing with saidcylinders, one of said closed ends being connected to said grid wherebysaid resonator is divided into a cathode-grid region and an anodegridregion, and the other of said closed ends being connected to said anodewhereby said structure defines a multiply folded feedback path forguiding waves from said anode-grid gap to said cathode-grid gap inproper phase and magnitude to sustain oscillations in said resonator,said cathode and anode having high frequency connections to spacedpoints on said resonator.

8. High frequency apparatus comprising a cylindrical cavity resonator,an electric discharge device within said resonator having a plurality ofelectrodes including a cathode, a grid, and an anode definingcathode-grid and anode-grid gaps, said cathode and anode having highfrequency connections to the ends of said resonator, a conductivestructure comprising at least two cylinders having a common closed endat one end thereof and positioned concentrically within said resonator,and at least one cylinder having a closed end and concentricallyintermeshing with said cylin ders, one of said closed ends beingconnected to said grid whereby said resonator is divided into acathode-grid region and an anode-grid region,

8 x and the other of said closed ends being connected to said anodewhereby said structure defines a multiply folded feedback path forguiding waves from said anode-grid gap to said cathode-grid gap inproper phase and magnitude to sustain oscillations in said resonator.

ANATOLE M. GUREWITSCH.

REFERENCES CITED The following referenlces are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,207,846 Wolff July 16, 19402,272,211 Kohler Feb. 10, 1942 2,351,895 Allerding June 20, 19442,353,742 McArthur July 18, 1944 2,404,261 Whinnery July 16, 19462,429,811 Guarrera Oct. 28, 1947

